Sensor system for fluid detection and discrimination

ABSTRACT

A light transmitting optical fiber shines light at a side edge portion of a hemispherical lens. The light is transmitted along the periphery of the lens to a second side edge portion located opposite the first side edge portion. A light sensitive component detects light at the second edge portion which light resulted from the light transmitted at the first side edge portion. The intensity of light detected at the second side edge portion is indicative of the fluid to which the lens is exposed, and can be evaluated and signaled by a microprocessor.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.11/852233, filed Sep. 7, 2007, issuing as U.S. Pat. No. 8,084,731 onDec. 27, 2011, which claims the benefit of Provisional application No.60/843515, filed Sep. 9, 2006, the disclosures of which are herebyexpressly incorporated by reference herein.

BACKGROUND

U.S. Pat. No. 5,712,934, issued Jan. 27, 1998, describes a “Fiber OpticInfrared Sensor” to detect the presence of water (as compared to air) oranother fluid having a refractive index substantially greater than air.Such system uses a return bent optical fiber. Light is transmitted intoone end of the fiber, and a photosensitive component provides a measureof the intensity of light leaving the other end. As described in suchpatent, the intensity of light sensed at the output end provides anindication of the presence of water or another fluid at the bend of thefiber. This technology has been in use in the “EOS” (environmentaloptical sensor) product available from Cambria Corporation of Seattle,Washington. Other fiber optic sensing systems are described and cited inU.S. Pat. No. 5,712,934.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This summary is not intended to identify key features ofthe claimed subject matter, nor is it intended to be used as an aid indetermining the scope of the claimed subject matter.

The present invention provides a novel, optical sensing system which, inone application, can be used to detect the presence of liquid (such aswater, alcohol, petroleum products, or a mixture thereof) between thewalls of a double-walled underground fuel tank. For example, if groundwater seeps through the outer wall, it will be detected; and if a fuelproduct leaks through the inner wall, the fuel will be detected.

In one aspect of the invention, a sensor uses a generally hemisphericallens of optically translucent material formed integral with a flatannular peripheral flange. The lens-flange component is mounted in adepression (recess, socket, countersink) of a special holder. The holderis formed with precisely positioned holes for snugly receiving the endportions of two optical fibers, such that the flat ends of the fibersare centered along opposite sides of the curved lens. A lighttransmitter sends light through one of the fibers and a light detectorreceives light from the other fiber. A microprocessor evaluates theintensity of the detected light and can generate a corresponding digitalsignal that indicates the fluid medium to which the lens is exposedbased on the attenuation of light intensity from the transmitter to thedetector.

In another aspect of the invention, an array of vertically spacedsensors is provided, each shielded from direct contact along alongitudinal direction of a housing for the sensors.

In another aspect of the invention, a special “detangler” is providedfor receiving and holding the end portions of the optical fibersopposite the end portions adjacent to the lens(es). The detanglercomponent is easily attachable to a mating connector of a circuit boardhaving a microprocessor to provide power to light emitting componentsand detect intensity of light returning to photosensitive components.

In another aspect of the invention, a special “tamper” feature isincorporated at the distal end of the sensor housing to provide anindication of whether or not the housing has left a predeterminedposition.

In other aspects of the invention, a sensor lens can be coated with acomposition suitable to enable detection of a target fluid. The coatingcan affect the optical performance of the sensor lens and/or react withthe target fluid in such a way as to affect the intensity of light thatis received by the detector.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 (prior art) is a diagrammatic side elevation of a double-walledtank having a known sensor system for liquid detection, with parts shownin section;

FIG. 2 (prior art) is a perspective of the sensor component of FIG. 1with parts in exploded relationship; and

FIG. 3 (prior art) is a side elevation of the sensor component of FIG. 1and FIG. 2 with parts assembled and parts shown in section;

FIG. 4 is a top perspective of a sensor system for fluid detection anddiscrimination in accordance with the present invention;

FIG. 5 is a top perspective corresponding to FIG. 4, but with partsshown in exploded relationship;

FIG. 6 is a side elevation of the sensor system of FIGS. 4 and 5 withthe parts assembled and parts shown in section;

FIG. 6A is a diagram of an anti-tamper process that can be used with thepresent invention;

FIG. 7 is an enlarged, somewhat diagrammatic, top perspective ofcomponents of the new sensor system in accordance with the presentinvention;

FIG. 8 is a longitudinal section of such components; and

FIG. 9 is a section corresponding to FIG. 8 with parts in differentpositions;

FIG. 10 is a top perspective of parts of an optical sensor in accordancewith the invention;

FIG. 11 is a top perspective corresponding to FIG. 10, with parts shownin exploded relationship;

FIG. 12 is a longitudinal axial section thereof; and

FIG. 13 is a front end elevation thereof;

FIG. 14 is a very diagrammatic, enlarged, fragmentary longitudinalsection of the distal end portion of a sensor in accordance with thepresent invention;

FIG. 15 is a graph illustrating aspects of operation of a sensor inaccordance with the present invention;

FIG. 16 is a diagrammatic side elevation of another embodiment of asensor in accordance with the present invention, with parts broken away;

FIG. 17 is a diagrammatic top perspective of component parts of anotherembodiment of a sensor system in accordance with the present invention;

FIG. 18 is a fragmentary top perspective of a multiple sensor systemusing component parts in accordance with FIG. 17; and

FIG. 19 is a longitudinal section of a modified sensor in accordancewith the present invention.

DETAILED DESCRIPTION

The optical sensor system shown diagrammatically in FIGS. 1, 2, and 3 isa prior art system sold under the trademark “EOS” (environmental opticalsensor) by Cambria Corporation of Seattle, Washington. Such sensor isbased on the construction and principles described and cited in U.S.Pat. No. 5,712,934. As for the drawings of the present invention (FIGS.4-19), the dimensions in FIGS. 1-3 are exaggerated for ease ofillustration and description.

FIG. 1 illustrates an underground tank T having inner and outer walls10, 12 with a vertical space 14 between them. In the known EOS system, aperforated mounting pipe 16 extends vertically through the space 14 fromthe metal bottom 18 of the outer tank to the top of the tank. Typically,only air is in the space 14 between the tank inner and outer walls.Perforations 20 (shown diagrammatically) of the upright mounting pipe 16permit liquid to enter the pipe in case of a malfunction, such asentrance of water from the exterior of the tank or leakage of fuel fromthe interior.

The sensor system includes a cylindrical housing 22 somewhat looselyreceived in the pipe 16. The bottom or distal end portion 24 of thehousing is shaped with vertically spaced V grooves 26 such that thedistal end portion resembles a partially opened accordion fold, althoughit is rigid, such as a rigid plastic. A narrow foot 28 at the bottomrests on the metallic bottom 18 of the outer wall. Individual opticalsensors 30 of the type described in U.S. Pat. No. 5,712,934 are spacedvertically along the distal end portion 24. An output cable 32 extendsfrom the housing 22, upward and out of the tube 16 for connection toappropriate equipment for receiving the outputs from the sensor system.Such outputs indicate whether or not water or fuel is present in theportion of the tube 16 in which the sensors 30 are mounted.

Details of the prior art sensor construction are shown in more detail inFIGS. 2 and 3. The narrow sensor foot 28 can contain a magnet 36. Suchmagnet interacts with a reed switch mounted at the bottom of themounting pipe to indicate that the sensor housing 22 is located at thebottom. Wires from the reed switch (not shown) extend upward along thesensor, to the top of the mounting pipe for an additional,position-indicating output.

The distal end portion of the housing is hollow, and the individualsensors 30 have cylindrical holders 38 that receive a length of opticalfiber 40. One stretch of the fiber extends lengthwise through its holderto an exposed return bend 42 which leads to the other stretch of thefiber. The fiber ends have cylindrical sleeves 44 sized to fit insocketed protrusions 46 of a coupler 48. Such coupler has pins 50 tomate with a standard connector 52 from a printed circuit board 54 onwhich a microprocessor 56 is mounted. During assembly, programmingaccess to the microprocessor is provided by way of a standard coupling58. Output wires 60 extend to and through the output cable 32. The cablecan terminate at a standard multipin connector 33.

The top or proximate end portion of the housing can include one or moreinterfitting cylindrical shells 62 and a top or proximate end cap 64with a hollow hub portion 66 through which the cable 32 extends. Theshell(s) are designed to hold the circuit board stably in position and,after assembly, the interior can be filled with potting material.

The socketed protrusions 46 of the coupler 48 contain, alternately, alight source (such as a light emitting diode) and a photosensitivedevice (such as a photodiode). For each individual sensor 30, one lengthof its optical fiber 40 extends from a light source and, by totalinternal reflection, carries light to the respective bend 42. Dependingon the medium to which the bend is exposed, light returns by way of theother length 40 of the fiber, which leads to the photosensitivecomponent. The photosensitive component provides an indication of theintensity of light received. This information is analyzed by themicroprocessor which indicates characteristics of the fluid to which thebend 42 of the sensor is exposed, by way of appropriate signals throughthe output wires 60.

In general, and without repeating the detailed description from U.S.Pat. No. 5,712,934, highly efficient transmission of light by totalinternal reflection may be obtained in a length of optical fiber.Nevertheless, light losses may result from, for example, refractive lossresulting from incident light striking the fiber wall at less than thecritical angle. Additional losses may be attributed to opticalimpurities present within the fiber, which may scatter or absorb light.In addition, the attenuation of light intensity through an opticalfiber, particularly a bent fiber, may result from engagement with amedium having a refractive index substantially different than that ofthe fiber. In the system of U.S. Pat. No. 5,712,934, light loss at thereturn bend of the fiber is much greater for water than for air, anddetectably different for gasoline than for either water or air. Manydevices and methods, in addition to that of U.S. Pat. No. 5,712,934,take advantage of the attenuation of light intensity through alight-conducting medium as a consequence of engaging an opticalcomponent with a medium such as a liquid.

In the system of FIGS. 1, 2, and 3, wires 60 include a power input wire,a ground wire, and various output wires to transmit signals thatindicate whether or not the sensors detect air, water, or gasoline. Thisprovides an environmental safeguard for a defective or damaged fueltank.

With reference to FIGS. 4, 5, and 6, the sensor system 100 in accordancewith the present invention has components similar to the earlier EOSSystem, but the later EOS version which is the subject of the presentapplication has several important differences. The cylindrical housing122 can include separate interfitting shells 162, a bottom or distal endportion 124, and a top or proximate end cap 164 with the central hub 166for the output cable 132. Individual sensors 130 are mounted in thegrooves 126 of the bottom housing portion 124 for exposure to the areaof interest. The foot 128 is much wider than the narrow foot of theearlier design. Foot 128 has a horizontal diameter or extent at least asgreat as the section of the housing within which the bottom sensor 130 bis mounted. Thus, the larger foot 128 acts as a shield that preventsengagement of the bottom sensor against the mounting pipe and/or anyother object as the sensor housing is moved longitudinally downward.

As shown diagrammatically in FIGS. 5 and 6, one or more Hall effectsensors 200 are mounted in the foot 128. One or more magnets 202 (showndiagrammatically in FIG. 6) are placed or secured in the bottom of themounting pipe, such that, when the housing is properly placed at thebottom of the pipe, the Hall effect sensors will detect the presence ofthe magnets and convey a signal to the microprocessor by way of a wireharness 204 and mating connectors 206. Thus, the microprocessor canreceive and supply a signal which will indicate whether or not the Halleffect sensors, once actuated by the magnets, have been moved.Programming of the microprocessor can provide an alarm signal along oneof the output wires 60. If desired, once “tripped” by movement from thepredetermined operating position, the system alarm may indicate a defectthat must be corrected by resetting the microprocessor before the systemis again operable. This will prevent tampering going undetected, such asif an individual tries to remove or lift the sensor to avoid signaling adangerous water-present or fuel-present condition.

FIG. 6A is a diagram of the anti-tamper process. Upon activation of thesystem (start box 201) a decision is made at 203 as to whether or notthe desired proximity condition is detected. In the describedembodiment, this is determined by whether or not the Hall effect sensorin the foot detects the presence of the magnets in the bottom of themounting pipe. If so, the process recycles back to the decision box. Ifproximity is not detected, indicating that the device has been movedupward away from the bottom of the mounting pipe, an alarm is activatedat 205. Next, a decision is made as to whether or not the system hasbeen reset (decision box 207). If it has not, the alarm is continued at209 and the process recycles to the decision at 207. It is only afterreset of the system that the process cycles back to the decision at 203as to whether or not the device is properly located at the bottom of thetube. It is envisioned that the reset process be sufficientlycomplicated that a trained technician is required in order to achievethe reset. In that case, tampering with the device will be indicatedpromptly and continuously, even if the device is moved back to itsnormal operating position, unless the technician has examined thesituation and determined that reactivation of the system is appropriate.

The new sensor component 130 is best described with reference to FIGS.10-14. The modified holder 138 has an exterior shape similar to theholder of the prior art system, including a cylindrical body that fitswithin the appropriate hole of the housing bottom or distal end, anannular shoulder to limit insertion of the holder into the housing, andan outward projecting cylindrical portion 208 which, at its outer end,has a shallow cylindrical recess or socket 210. The holder can be formedof aluminum. Two holes 212 extend lengthwise through the holder, 180°apart and equidistant from the center. A generally hemispherical lens214 and a thin, flat, annular base 216 are formed integrally from anoptically translucent material, such as clear or nearly clear glass. Thelens is approximately a hemisphere with a slight flattening at the apexon the exterior side which is located for exposure to the area ofinterest. In a representative embodiment, the hemisphere base radius canbe represented as R and the radius of curvature at the apex nR, where nis a value less than 1.00 but greater than 0.90. Still morespecifically, in a representative embodiment, the radius of curvature ofthe lens at the base is 1.46 mm; the radius of curvature at the apex is1.43 mm; the thickness of the flat base is 0.25 mm; and the diameter ofthe base can range from 5.67 mm to 5.92 mm. The diameter of the socket210 is nearly identical to the diameter of the base 216 so that the lens214 is precisely positioned in the socket. With reference to FIGS. 12and 13, the holes 212 also are precisely positioned so that alongitudinal continuation of the edge of the lens (such edge meets thebase at an angle of 90° or very close to 90°) will intersect the holes.In a preferred embodiment, the holes are centered at opposite sides ofthe periphery of the lens such that each hole has a portion projectingbeyond the exterior of the lens and a portion projecting inward of theexterior of the lens. Optical fibers 140 are closely received in theholes and secured therein (in a representative embodiment, the diameterof each fiber is approximately 1 mm).

FIG. 11 illustrates the fibers 140 insertable into the holes 212. Fromits distal end adjacent to the inner surface of the lens component(opposite the exterior side and remote from the area of interest), onefiber extends to a light source, diagrammatically represented at 220.Infrared light (representative wavelengths of 940-960 nanometers) istransmitted through the fiber 140 by total internal reflection, and outthe opposite end (directed at the inner surface of the lens), asdiagrammatically represented in FIG. 14. Depending on the medium towhich the exterior of the lens is exposed, more or less of the lighttravels along the periphery of the lens, as represented by the brokenlines 214 in FIG. 14. The light waves may travel along the exterior lensin an evanescent mode and/or along the interior of the lens in awhispering gallery mode, or due to multiple refractive reflections. Inair, a significant portion of the light intensity travels to theopposite side of the lens, then into the other optical fiber 140 andback to a photosensitive component 222 (FIG. 11) such as a photodiode.The photosensitive component provides an output that changes as afunction of the intensity detected. For the present invention, FIG. 15represents the difference in intensity detected depending on whether themedium surrounding the lens is air (high intensity; point A), water(moderate intensity; point B), alcohol (detectably lower intensity;point C), or gasoline (very low intensity; point D). For example,experiments using a sensor system as described above, indicate thatlight detected by a photodiode at the “output side” of a lens exposed toair has an intensity about 3.5 times that of a lens exposed to water.For alcohol, the intensity is approximately 80% that of water. Forgasoline, the detected intensity is much less than one-half theintensity for water. These values are easily convertible to digitalvalues by the microprocessor to indicate the medium to which the lens isexposed. Stated in another way, the microprocessor evaluates theintensity at the detector side and provides an indication of the fluidmedium to which the sensor is exposed, such as air, water, alcohol, orgasoline.

Known optical sensors rely on refractive losses and do not deliberatelyuse lenses that intersect the cross-section of an optical fiber. In thepresent invention, it is important that such intersection be provided,i.e., that at least a significant portion, preferably one-half thediameter, of each optical fiber be positioned to the outside of the lensperiphery, particularly the light transmitting fiber. Otherwise, thediscrimination (contrast) of the output is jeopardized.

Returning to FIG. 5, the free ends of the optical fibers 140 from thesensors 130 preferably are held in a detangler ring 230. The details ofsuch ring, the fibers received therein, and the connection 148 to whichit couples, are best seen in FIGS. 7, 8 and 9. Referring to FIG. 8(cross-section), the detangler ring 230 has several cylindricalprojections 232, one for each of the fibers 140 from the sensors. Withineach projection 232, there is a central, integral sleeve 234 having aninternal bore 236 almost precisely the same diameter as an optical fiber140. All of the fibers are inserted through their respective sleeves 234and severed even with the ends of the other fibers. With reference toFIG. 7, the severing of the fibers results in a slightly enlarged ornonuniform shape (represented at 145) which will not pass back throughthe sleeve without excessive tension being exerted. Toward the center ofthe sleeve, two connection prongs 240 project longitudinally in the samedirection as the cylindrical projections 232. Prongs 240 extend beyondthe projections 232 and have hooked ends 242.

The coupling 148 which mates with the new detangler ring 230 is verysimilar to the coupling of the prior art embodiment. Alternating lightemitting components (light emitting diodes) 220 and photosensitivecomponents (photodiodes) 222 are received in cylindrical protrusions 146that have cylindrical blind bores 244. As seen in FIG. 9, the detanglerring 230 and coupling 148 can be secured together by aligning the prongs240 with corresponding openings 246 of the coupling, and chamfers formedon the hooked ends of the prongs result in wedging them together untilthe hooked ends snap over the outside marginal portions of the openings246 as seen in FIG. 9. The blind bores 244 snugly receive the sleeves234 and position the optical fiber ends close to their photo emitting orsensitive elements. The printed circuitry on the back face 250 of thecoupling routes to the pins 150 which as seen in FIGS. 5 and 6 mate withthe connector 152 from the printed circuit board 154.

In other respects, the sensing system in accordance with the presentinvention is similar to the prior art EOS sensing system. Separate wires60 carry signals to and from the microprocessor, including power,ground, water detection, fuel detection, tamper detection (novel to thepresent invention), as well as binary transmit (TX) and receive (RX)signals for calibrating or reprogramming the microprocessor.

In the embodiment of FIG. 16, the distal end portion 324 of the housingfor the individual sensor 330 is the same as previously described. Thesensor has a holder 338 with an outward-facing recess or socket 310 ofthe type previously described. The lens 314 and integral base 316 areidentical to the corresponding components previously described, and aremounted in the recess for precise positioning of the lens. The holderhas through holes 312 sized and positioned as described for thepreceding embodiment.

In the embodiment of FIG. 16, however, the holder 338 is quite short.Holes 312 contain a short segment or stub of optical fiber 340 or otherlight transmissive material. The light emitting component (LED) 320 ispositioned directly adjacent to one of the stubs or sections 340 and thephotosensitive component (photodiode) 322 is positioned directlyadjacent to the other stub or section. A printed circuit board 354 andmicroprocessor 356 are positioned close to the holder 338 and carry thephotosensitive and photo emitting components. Thus, there are separatephoto emitting and photosensitive components, as well as circuit boardsand microprocessors for each individual sensor. Power for the sensor canbe provided by a wire 380 and output signals supplied along one or morewires 382. The circuitry preferably is potted in a rigid or semi-rigidmaterial 384. Wires 380, 382 can lead to a central circuit and/ormicroprocessor for evaluation and signaling along a cable, similar tothe output cable of the embodiment previously described, to indicate thefluid to which a sensor is exposed.

FIGS. 17 and 18 diagrammatically illustrate another sensor system 400similar to the previously described systems. Referring first to FIG. 18,individual sensors 430 are spaced along the length of a housing 424. Thehousing is hollow, and at least one side has slots or openings 470 forreceipt of drawer-like sensor holders 438. Each holder can contain theprinted circuit board 454 with microprocessor and output leads, as wellas an individual, light emitting component 420 and light sensitivecomponent 422. With reference to FIG. 17, the lens 414 for theembodiment of FIGS. 17 and 18 is a semi-cylindrical shape, preferablyformed integral with a thin, flat base 416 resembling tabs or wingsextending oppositely from the lens. This configuration is mounted in arecess or socket 410 in the exterior face of the holder 438. The lightemitting and light sensitive components are positioned precisely so asto be intersected by a continuation of the opposite sides of thesemi-cylindrical lens, which extend at angles of 90°, or close to 90°,to the exterior face of the holder 438. Dimensions for the lens andintegral base can be the same as the dimensions for the hemisphericallens and flat base previously described, with respect to radii ofcurvature, and measured intensity by the light sensitive component isessentially the same as shown in FIG. 15, based on the transmissionillustrated diagrammatically in FIG. 14.

An additional modification for a lens used in the system of the presentinvention is shown diagrammatically in FIG. 19. The exterior side oflens 514 has a thin outer coating 515 of a composition that affects theintensity of light received at the detector side. The coating can affectthe optical performance of the sensor by affecting the degree ofattenuation from the transmitter side to the detector side and/or reactwith a target fluid, such as by fluorescence. This embodiment can beadapted (by selection of an appropriate coating) to indicate thepresence of a specific vapor, for example, or a class of vapors.Representative examples are ammonia compounds, and rocket fuel(hydrazine and variants). Representative coatings are dyes that exhibitfluorescence in the presence of the target fluid, such as xanthene dyesor triphenylmethane dyes, which can be incorporated in a liquid plasticcarrier, such as polyvinylchloride, for application to the exterior ofthe lens. The coating can be very thin, such as 5 to 15 microns. Theexact composition of the coating 515 will depend on the particulartarget fluid to be detected. The fluorescent properties of therepresentative dyes, for example, vary depending on the environment andcan be used in the present invention to achieve a significant variationin light intensity at the detector side, which is evaluated by themicroprocessor that provides the indication of the presence or absenceof the target fluid.

Other than the coating 515, the FIG. 19 sensor embodiment is identicalin construction to the embodiment of FIGS. 10-12. The same coating canbe used in systems of the types shown in FIG. 16 and FIGS. 17-18 fordetection of a target vapor.

While illustrative embodiments have been illustrated and described, itwill be appreciated that various changes can be made therein withoutdeparting from the spirit and scope of the invention.

1. A sensor assembly for fluid detection and discrimination in an areaof interest, said assembly comprising: a lens component having an outerperiphery with a substantially semi-circular cross-including a centralapex, and first and second side edge portions disposed at oppositesection sides of the apex and extending approximately parallel to eachother, the lens component having an inner surface located opposite theouter periphery; a holder in which the lens component is mounted forexposure of the lens outer periphery to an area of interest; alight-transmitting component mounted in the holder remote from the areaof interest and transmitting light toward the inner surface of the lensand at the first side edge portion of the lens; a light sensitivecomponent mounted in the holder remote from the area of interest todetect light emitted at the inner surface of the lens adjacent to thesecond side edge portion as a result of light from thelight-transmitting component at the first side edge portion.
 2. Thesensor assembly defined in claim 1, in which the light transmitted bythe light-transmitting component includes light at the interior of thelens periphery and light at the exterior of the lens periphery.
 3. Thesensor assembly defined in claim 2, including means for detecting theintensity of light received at the light sensitive component and forproviding an indication signal of a characteristic of a fluid in thearea of interest as a function of the detected intensity.
 4. The sensorassembly defined in claim 2, in which the light sensitive component is alight intensity detector, and including a microprocessor evaluating theintensity detected by the light detector and providing a signalindicating the presence or absence of a fluid of interest based on thedetected intensity.
 5. The sensor assembly defined in claim 4, in whichthe microprocessor provides a signal indicating the presence or absenceof two or more of water, air, alcohol and gasoline.
 6. The sensorassembly defined in claim 4, in which the microprocessor provides asignal indicating the presence or absence of two or more of water, air,alcohol and a fuel.
 7. The sensor assembly defined in claim 1, in whichthe lens outer periphery has a coating that affects the intensity oflight emitted at the inner surface of the lens adjacent to the secondside edge portion as a result of light from the light-transmittingcomponent at the first side edge portion.
 8. The sensor assembly definedin claim 7, in which the coating is a composition that affects theamount of attenuation in light intensity from the light transmittingcomponent to the light sensitive component.
 9. The sensor assemblydefined in claim 7, in which the coating is a composition that reactswith a fluid of interest.
 10. The sensor assembly defined in claim 7, inwhich the coating is a composition that exhibits fluorescence in thepresence of a fluid of interest.
 11. The sensor assembly defined inclaim 7, in which the coating is a composition that exhibitsfluorescence in the presence of a fluid selected from the group ofammonia compounds and hydrazine.
 12. The sensor assembly defined inclaim 7, in which the coating is a composition selected from the groupof xanthene dyes and triphenylmethane dyes.
 13. The sensor assemblydefined in claim 7, in which the coating contains an ingredientincorporated in a liquid plastic carrier.